Field of the Invention
The present invention relates to an ultrasonic motor, in particular to a linear drive ultrasonic motor and to an optical apparatus including the same.
Description of the Related Art
A technique has been known where, in a conventional linear drive ultrasonic motor (hereinafter, called a linear ultrasonic motor), a piezoelectric element for generating periodical vibrations in an ultrasonic range by applying a high frequency voltage is adopted as a vibration element, and a slide member pressed thereagainst is driven by the vibrations.
For instance, as a linear ultrasonic motor, a configuration disclosed in Japanese Patent Application Laid-Open No. 2001-292584 is exemplified. This configuration has a function of supporting a vibration node portion of a vibration body (a vibration element in the present invention), and a function of pressurizing the vibration body to cause a frictional force between the vibration body and a rail (a slide member in the present invention). These functions are achieved by using one spring member and a plurality of rubber sheets and incorporating the spring member between a fixing plate and the vibration body via the rubber sheets The vibration element is pressed against the rail. As a result, ultrasonic vibrations of the vibration body frictionally drive the rail. At this time, a rotational member is arranged on a surface of the rail opposite to a portion in contact with the vibration body, and supports the rail such that the rail can move while reducing the sliding resistance of the rail. The rail is thus sandwiched between the vibration body and the rotational member, thereby achieving a configuration where the pressure contact power is closed between the fixing plate and the rail.
In the case of adopting a configuration as disclosed in Japanese Patent Application Laid-Open No. 2001-292584, the rotational member, the rail, the vibration body, the spring member and the fixing plate are arranged in series in the pressurizing direction. This arrangement causes a problem of increasing the thickness of a motor including a drive unit and a unit to be driven.